Butterfly Needles in Phlebotomy: When to Use Them, Gauges and Safety
By the OQMPS team ·
A butterfly needle is a short, thin needle with flexible plastic “wings” on either side and a length of tubing behind it. Its proper name is a winged blood collection set, and you will also hear it called a winged infusion set. Phlebotomists reach for one when a vein is small, fragile or hard to reach, such as on the back of the hand, and for young children and many older adults.
This guide covers how a butterfly works, when to use one, which gauge to choose, what the research says about the samples it collects, and how to use it safely.
Butterfly needles at a glance
- Gauges: 21, 23 and 25 are standard for blood collection. The higher the number, the thinner the needle.
- Size: a 0.75-inch needle, with 7 or 12 inches of tubing (BD’s push-button sets).
- Best for: small, fragile or hand veins, children, and patients with difficult veins.
- Watch for: draw a discard tube first if a light blue (citrate) tube is the first tube, and activate the safety feature before disposal.
How a butterfly needle works
A standard venipuncture uses a straight needle screwed into a tube holder: the needle, holder and tube are one rigid unit. A butterfly separates them. You hold the needle by its wings, which keeps your fingers close to the skin and lets you insert at a shallow angle into a small or superficial vein. The tubing carries the blood back to a tube holder, so changing tubes does not move the needle in the vein.
When the needle enters the vein, a flash of blood appears in the tubing, confirming you are in. Modern sets include a safety feature: BD’s push-button set, for example, “provides single-handed, in-vein safety activation to instantly retract the needle after use.”
When do phlebotomists use a butterfly needle?
For most adults with good antecubital veins, the straight needle and tube holder remain the conventional method. A butterfly earns its place when the vein calls for more control:
- Hand veins. CLSI lists the back of the hand among the preferred venipuncture sites, and its small, superficial veins suit a butterfly’s shallow approach.
- Small or fragile veins, common in older patients and anyone whose veins are thin or roll easily.
- Children, whose veins are small and who may move.
- Difficult draws, where a straight needle has not worked or is unlikely to.
If you are the patient
If your blood was drawn with a butterfly, it is simply the tool your phlebotomist picked for your veins, and as the research below shows, the sample is just as good. If your veins have been hard to draw from before, say so: it helps the phlebotomist choose the right needle.
Does it hurt less? Butterflies are often described that way because the smaller gauges are thinner, but we found no good research showing it for adults. A butterfly is chosen to suit the vein, not to reduce pain.
Butterfly needle vs straight needle
| Feature | Butterfly (winged set) | Straight needle and tube holder |
|---|---|---|
| Best for | Small, fragile or hand veins; children; difficult draws | Routine draws from good antecubital veins |
| Gauges | 21, 23 or 25 | Commonly 21 |
| Sample quality | No difference in hemolysis at 21 gauge (2005 study) | The conventional method it was compared against |
| Discard tube | Needed if a citrate tube is drawn first | Not needed for the tubing |
| Share of reported needlesticks | 4.3% (EPINet, 2024) | 1.2% (EPINet, 2024) |
Which gauge to choose
Needle gauge runs backwards: a 25-gauge needle is thinner than a 21. The rule of thumb is to use the largest gauge the vein comfortably allows.
| Gauge | Size | Typical use |
|---|---|---|
| 21 G | Largest of the three | Veins that can take it; the same gauge as a typical straight needle |
| 23 G | Medium | Smaller veins |
| 25 G | Smallest | Newborns and patients with very difficult veins only |
The 25-gauge guidance comes from research: a 2006 study found more variability in potassium results with 25-gauge needles than 23-gauge, and its authors concluded that needles of 25 gauge or smaller “cannot be universally recommended” and should be kept for patients with problematic venous access and newborns.
Does a butterfly needle affect the blood sample?
Not when it is used properly. A 2005 study drew blood from 30 outpatients with both a 21-gauge straight needle and a 21-gauge butterfly. Hemolysis, the breakdown of red cells that can spoil a sample, was not statistically different between the two. Of 43 tests, only sodium, white cell count and platelet count differed, and the authors concluded that with proper technique the butterfly “may be a reliable alternative to the conventional straight needle.”
The gauge matters more than the device. The 2006 study above found broad variation in free hemoglobin, a marker of hemolysis, with the smaller needles, which is another reason to use the largest gauge the vein allows.
The discard tube
The butterfly’s tubing is full of air when you start. The first tube you fill takes that air in and ends up short. For most tubes that is not a problem, but a light blue citrate tube needs the right ratio of blood to anticoagulant for clotting tests.
So when a butterfly is used and the citrate tube is the first one needed, BD’s guidance is to draw a discard tube first: a plain or another citrate tube that fills the tubing’s “dead space” and is not tested. It does not need to be full. The rest of the draw follows the usual order of draw.
Needlestick safety
Butterflies show up in injury reports more often than standard blood-collection needles. In the 2024 EPINet report, which pools sharps injuries from 39 U.S. hospitals, winged steel needles accounted for 83 of the 1,940 injuries where the device was recorded (4.3%), against 23 (1.2%) for vacuum tube holder needles. (The report counts injuries, not how often each device is used, and winged needles are also used for infusions.)
Safety features only help if they are used. Of the injuries the same report recorded from safety-designed devices, the mechanism had not been activated in 63.9%. Activate the safety feature as soon as the needle is out, or in the vein if the device is designed for that, and never recap: OSHA’s Bloodborne Pathogens Standard says contaminated needles “shall not be bent, recapped, or removed” except in narrow circumstances.
Using a butterfly needle, step by step
- Identify the patient with two identifiers, and choose the vein and the gauge.
- Apply the tourniquet for no more than one minute before you access the vein, as CLSI requires.
- Clean the site with 70% isopropyl alcohol, using friction, and let it air dry.
- Attach the set to a tube holder, hold the needle by its wings, and anchor the vein below the site.
- Insert at a shallow angle and watch for the flash in the tubing.
- Fill the tubes in the order of draw, with a discard tube first if the citrate tube leads, and invert each one as you go.
- Release the tourniquet, withdraw the needle, activate the safety feature and apply pressure.
- Discard the whole set, tubing and all, in a sharps container straight away, and label the tubes in front of the patient.
Butterflies take practice: the short needle and flexible tubing feel different from a straight needle, and small veins leave less room for error. That is why hands-on training matters.
Practice with OQMPS
Hands-on phlebotomy classes in Arizona, Oregon, Texas, Utah and Washington, 3 days in class plus self-paced home study. Preparing for your exam? Try our free phlebotomy practice test.
Frequently asked questions
What is a butterfly needle used for?
Drawing blood from small, fragile or hard-to-reach veins, such as hand veins, and from young children and many older adults. Its wings and tubing give the phlebotomist more control than a straight needle on a tube holder.
Does a butterfly needle hurt less?
Butterflies are often described as less painful because the smaller gauges are thinner, but we found no good research showing it for adults. Phlebotomists choose a butterfly to suit the vein, not to reduce pain.
What gauge is a butterfly needle?
Butterflies for blood collection come in 21, 23 and 25 gauge. The higher the number, the thinner the needle. Research supports keeping 25 gauge for newborns and patients with very difficult veins.
Does a butterfly needle cause hemolysis?
Not in itself. A 2005 study comparing a 21-gauge butterfly with a 21-gauge straight needle found no statistically significant difference in hemolysis. Smaller gauges are a different matter, so use the largest gauge the vein allows.
Why do you need a discard tube with a butterfly needle?
The tubing starts full of air, which would underfill the first tube. That matters for a light blue citrate tube, which needs a precise ratio of blood to anticoagulant, so a discard tube is drawn first when the citrate tube would otherwise lead.
Are butterfly needles more dangerous for needlesticks?
They show up in injury reports more often: in the 2024 EPINet report, winged steel needles accounted for 4.3% of recorded sharps injuries, against 1.2% for vacuum tube holder needles. Activating the safety feature right away and never recapping are the main defenses.
Sources
- BD, Vacutainer Push Button Blood Collection Set
- Lippi et al., Preanalytical variability in laboratory testing: influence of the blood drawing technique, Clin Chem Lab Med (2005)
- Lippi et al., Influence of the needle bore size used for collecting venous blood samples on routine clinical chemistry testing, Clin Chem Lab Med (2006)
- International Safety Center, EPINet Report for Needlestick and Sharp Object Injuries, 2024
- BD Vacutainer Order of Draw for Multiple Tube Collections
- ACA, New CLSI Venipuncture Guidelines (summary of CLSI GP41, 7th ed.)
- OSHA Bloodborne Pathogens Standard, 29 CFR 1910.1030
- The Joint Commission, National Patient Safety Goals (hospital program)